Fluorodeoxyglucose (FDG) positron emission tomography (PET) imaging is useful in the detection of lymph node metastases including, for instance, lung cancer, head and neck tumors, and esophageal cancer. In particular, qualitative image interpretation of FDG PET images has been useful for tumor detection and staging. Further, FDG PET measurements have been applied to identify the response of malignant tumors to therapy.